1. Field of the Invention
The present invention relates to an inkjet printer. More particularly, the present invention relates to a method and apparatus for correcting deviation of a temperature sensor placed in a header having a plurality of nozzles in an inkjet printer.
2. Description of the Related Art
Inkjet printers spray ink through a plurality of nozzles placed in a header by driving heaters placed in the header. Although the same driving pulse signal is applied to the header, a different amount of ink is sprayed based on a substrate temperature of the header. Since a print quality is affected by the substrate temperature of the header, there is a need for a printer to correctly detect a temperature in order to apply a driving pulse signal suitable for the temperature. For example, when it is low in temperature, the substrate is heated to increase the temperature. Conversely, when it is high in temperature, the driving pulse signal is decreased or the printer waits until the temperature falls.
Generally, a thermistor is used as a temperature sensor for sensing the temperature of the inkjet printer header. The thermistor is a thermally sensitive resistor whose resistance is changed sensitively according to change of a temperature. A voltage output from the thermistor is amplified in order to measure the temperature of the header. Then, the amplified analog output voltage is converted into a digital form. The temperature of the thermistor, that is, the temperature of the header can be measured based on the digitized output voltage. Normally, there is large deviation of ±20% in the thermistor. Thus, there is a need to correct the deviation of the thermistor for more accurate temperature readings.
For example, U.S. Pat. No. 6,628,906, entitled “Image forming apparatus with temperature based control” discloses an image forming apparatus for sensing a temperature using such a thermistor.
As described above, it is needed to correct the deviation of the thermistor in the printer. In order to correct the deviation, a relatively high-priced ambient sensor, which is a sensor for sensing an ambient temperature, is placed in an engine board which is a main board of the printer. In order to correct the deviation of the thermistor in the printer having the ambient sensor, the voltage of the thermistor in the header is firstly measured. The output voltage from the thermistor corresponding to a current temperature is found by reading the accurate ambient sensor with respect to the measured voltage. Therefore, since the deviation of each thermistor is measured, the measured temperature of the thermistor can be corrected.
As described above, an IC (Integrated Circuit) type ambient sensor is additionally used in the engine board, in order to correct the deviation of the thermistor for sensing the temperature of the header in the conventional inkjet printer. However, there is a drawback that such an ambient sensor is expensive, even though it is accurate. Another drawback is that the printer circuit configuration is complicated.